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For an arithmetical sequence the first term is ... - JAMB Mathematics 1992 Question

For an arithmetical sequence, the first term is 2 and the common difference is 3. Find the sum of the first 11 terms
A
157
B
187
C
197
D
200
correct option: b

a = 2, d = 3 and n = 11

To find Sn/sub> = (\frac{n}{2}) [2a + (n - 1) (\delta)]

= (\frac{11}{2}) [2(2) + (11 - 1) 3]

= (\frac{11}{2})n [4 + 10(3)]

= (\frac{11}{2})(34)

= 11 x 17

= 187

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